240 



THE ELASMOBRANCH FISHES 



terior and a posterior division. These divisions supply the inferior oblique and 

 the inferior rectus muscles as in Heptanchns. 



The relation of the nerve to the ciliary ganglion in some forms is interesting. 

 Sometimes this ganglion (or ganglia) is on the oculomotor nerve and is called 

 the ganglion oculomotoris. Or, again, it may be on a branch joining the gan- 

 glion of the ophthalmicus profundus with the oculomotor nerve. 



The trochlearis nerve, as we have said, has its nucleus in the mesencephalon. 

 Its fibers cross and pass out through the roof between the mesencephalon and 

 the cerebellum and go to innervate the superior oblique muscle of the eye. 



The trigeminal or fifth cranial nerve is composed of an anterior portio 

 minor and a posterior portio major. "While both of these roots contain motor 



Fig. 220. Cranial nerves, Squalus acanthias. (From Norris and Hughes.) 

 br.p., brachial plexus; bu.VII, buccalis of seventh; d.X, ramus dorsalis of tenth nerve; 

 gri., first spinal ganglion; hb., hypobranchial bundle; limd., hyomandibularis ; U.X, lateral 

 line nerve ; md.e.VII, mandibularis externus of seventh ; md.i.VII, maudibularis internus of 

 seventh; md.V, mandibularis of fifth; mx.V, maxillaris of fifth; op.V, ophthalmicus pro- 

 fundus; os.V, and os.FII, ophthalmicus superficialis of fifth and seventh; ph. IX, pharyn- 

 geal branch of ninth; pl.VII, palatinus of seventh; po.t., post-trematicus of ninth; pr.t., 

 pretrematicus of ninth; sp., spiracle; st.IX, supratemporalis of ninth; st.X, supratem- 

 poralis of tenth nerve ; vi.X, visceral nerve ; 1/ and 2, occipitospinal nerves ; II, optic ; ///, 

 oculomotor; IV, trochlearis; VI, abducens; VIII, auditory nerve. 



and sensory portions, motor fibers predominate in the anterior part and 

 sensory in the posterior root. The motor fibers arise from the visceromotor 

 nucleus in the medulla (vm.n., fig. 216) and are distributed principally to the 

 muscles of the jaws. The sensory fibers arise from various ganglia, such as the 

 ganglion of the ophthalmicus profundus, the ophthalmicus superficialis (Mus- 

 telus calif ornicus), and the gasserian ganglion. Sensation brought from the 

 region around the nose passes by the ganglion cells and on to the brain. 



In the Elasmobranchs the ganglia of the trigeminal and the buccal division 

 of the facial nerves are so intimately associated as often to be inseparable; 

 usually the former are more or less covered up by the latter. In Chlamydosel- 

 aclius, however (fig. 219) , the two are distinct medially (Hawkes, 1906) . From 

 the gasserian ganglion {g.) the large maxillaris and the mandibularis divisions 

 of the fifth nerve arise and from the small ganglion on the inner side of the 

 gasserian, the two smaller nerves, the ramus profundus {op.Y) and the ramus 

 superficialis {os.Y) of the fifth, take their origin. 



